Pillow: Heap buffer overflow in ImagingJpegDecode

Summary JpegImageFile.draft — which Image.thumbnail calls automatically — requests 1/2, 1/4 or 1/8 scaled JPEG output and shrinks self.size and the tile extents to match, so setimage allocates a single-row decode buffer of ceilW/s samples. ImagingJpegDecode sets cinfo.scalenum/scaledenom, calls...